The state is erecting a temporary bridge across the road as part of the $95 million Interstate 75 widening project in north Hillsborough and south Pasco counties. Traffic under the bridge will be narrowed to one lane in each direction.

The Department of Transportation is warning drivers to expect delays as workers slide the 320-foot span into place. A bulldozer will push the span inch by inch above the road during a three- to four-hour period, DOT spokesman John McShaffrey said Wednesday.

As the metal span, which looks like part of an overgrown Erector set, slides into place, workers below will shut down traffic.

"We're trying to warn people that if they're going to be using Bruce B. Downs out here, they're going to face some delays because whenever the contractor is pushing the bridge, we won't let traffic pass underneath," McShaffrey said.

Every 15 minutes or so, after traffic has backed up on Bruce B. Downs, workers will stop pushing the bridge and allow the traffic to flow freely again, he said.

Expect traffic to narrow to one lane in each direction starting at about 10 p.m. today and then shut down for 15-minute intervals starting at about midnight. Officials expect the work to be finished before Friday morning's rush hour.

Workers will slide the bridge using heavy-duty rollers and then set it atop concrete footings. Once that phase is complete, large steel plates will be fastened onto the bridge and covered with asphalt.

The work is part of a larger project to replace the interstate's northbound and southbound two-lane bridges with four-lane bridges.

The temporary span is expected to open for northbound I-75 traffic in April.

Northbound I-75 traffic will then be shifted onto the temporary bridge and southbound traffic will be routed onto the old northbound bridge, McShaffrey said. That will give crews enough room to demolish the southbound bridge and erect a new span in its place.